# `•signal` — Signal

`•signal kind` raises an error of the kind that `kind` names, and
`message •signal kind` gives it a message. Without one, the message is
“explicitly signalled”. An [error guard](../glyphs/error-guard.qmd)
catches the error in the same way as an error from a primitive.

``` bpl
positive←{⍵≤0?"must be positive" •signal "DOMAIN";⍵}
safe←{"DOMAIN"::0 ⋄ positive ⍵}
safe¯3    ⍝ 0
safe4     ⍝ 4
```

`kind` is the name of one of BPL’s kinds, which the error guard page
lists, or any other one-word name, which makes a kind of the program’s
own. Names are read in any case. `kind` can also be a caught error, such
as `$e`, and `•signal` raises its kind and message again at the
`•signal` call.

Errors: `DOMAIN` for a number, or a name that isn’t one word of letters,
digits and underscores.